Vine-like lianas alter the edges of fragmented forests: New study

A new study has found that a group of climbing plants called lianas spring up in higher numbers along the edges of fragmented forests than they do in less-disturbed patches.

Previous research has shown that lianas can cause trees to die or to stockpile less carbon, and they can also affect the mix of tree species present in the forest.

To ensure a healthy, functioning ecosystem, managers can set aside a buffer zone around the edges of these patches or increase the size of the protected area as a whole.

Carving up rainforests to make room for farming, ranching and other uses induces a host of changes into the ecosystem, many of which scientists are only just beginning to understand.

A recent study, looking at how vine-like plants colonize the edges of these ever-smaller forest fragments, adds a new piece to that puzzle. A team of ecologists reports that a group of climbing plants called lianas spring up in higher numbers along the edges of these bits of forest than they do in less-disturbed patches.

Lianas are similar to vines in that they latch onto trees as an energy-efficient way of climbing toward the forest canopy. As previous research has shown, lianas can cause trees to die or to stockpile less carbon, and their presence can also fiddle with the mix of tree species present in the forest. In doing so, they change the habitat for animals and other organisms that live there. In other words, changes in liana growth and numbers can fundamentally alter a forest’s structure and the way it functions, highlighting the importance of protecting forest edges.

When a tree falls or a patch of forest is cleared, it allows a rare dose of sunlight down to the forest floor, and lianas are naturally among the plants that crop up when these disturbances occur, said Mason Campbell, a botanist at James Cook University in Cairns, Australia, and lead author of the study.

“If you have a large expanse of forest, lianas are sort of like Band-Aids that fix a single treefall and [also] that seal the edge,” Campbell told Mongabay.

But when humans split up, or “fragment,” forests into smaller and smaller pieces, lianas become more numerous. They also penetrate deeper into the interior than in larger or more intact blocks of forest, Campbell and his colleagues found.

“They actually get into the treefall gaps, and they impede succession,” he said, meaning that they keep the forest from growing back as it normally would when trees within it or along its edge fall down. Those disturbances might occur when a farmer clears new land for agriculture, or when a cyclone — common where Campbell did his research in the north of Australia — knocks down a bunch of trees.

Mason Campbell, the study’s lead author, measures the diameter of a tree in the Atherton Tablelands. Photo by Mason Campbell/James Cook University.

A volcanic eruption thousands of years ago laid down a blanket of fertile soil across an area known as the Atherton Tablelands, giving rise to “some of the best rainforest” in Australia, Campbell said. Still today, it boasts the densest population of Lumholtz’s tree kangaroos (Dendrolagus lumholtzi) on the continent, and it’s part of the Wet Tropics of Queensland UNESCO World Heritage Site.

But the soil’s fertility also means it’s a prime place for farming and ranching, and over the years, people have cleared away a lot of the forest, leaving behind a smattering of forest fragments — “very bad for nature, but handy for studying,” Campbell said.

“It’s a bit like a natural laboratory,” he added.

To look at the impact of lianas, Campbell and his team compared both fragmented and intact forests in the Atherton Tablelands. Across their study plots, the team took fine-scale measurements of the tree canopy, and they counted the trees and measured their diameters. They also looked at the size and number of lianas present around the edges of these blocks. In general, the forest fragments had less canopy cover, leading to more lianas, as well as a different mix of liana species compared to what the researchers found at the intact forest sites. They published their work online on April 2 in the journal Ecology and Evolution.

These new revelations about lianas point to the need to manage forest fragments differently. In a place like the Atherton Tablelands, that could mean going beyond protecting areas of forest as tourist sites or remnants that show what the forest once looked like, Campbell said. To ensure a healthy, functioning ecosystem, managers could set aside a buffer zone around the edges of these patches or increase the size of the protected area as a whole, to safeguard the borders from the disturbances that encourage the infiltration of lianas and their impacts on the forest in the first place.